A monolithic pressure sensitive integrated circuit is a semiconductor chip in which there are combined a pressure sensitive diaphragm, its piezoresistors, and the circuitry used to process or condition the signal developed by the piezoresistors to make it useful for its designed purpose.
Pressure sensors are of particular use for automotive applications. An article entitled "A Pressure Sensor for Automotive Applications" by J. A. Oakes, Proceedings of the Third International Conference on Automotive Electronics, PPS. 143-149, 20-23 October, 1981, London, England, sponsored by the Institute for Mechanical Engineers, describes a pressure sensor for automotive applications that uses two separate chips and a hybrid substrate. One chip includes the sensitive pressure diaphragm and its associated piezoresistors; the second chip includes electronics for amplifying the signal received from the piezoresistors; and the hybrid substrate includes additional conditioning circuits. A monolithic chip to replace such two chips and hybrid substrate has a number of obvious advantages. A process for preparing a monolithic pressure sensor which combines both the pressure sensitive elements and conditioning electronics is described in U.S. Pat. No. 4,618,397 that issued on Oct. 21, 1986.
However, the present invention in one aspect is a process for making a monolithic pressure sensor by a different process believed to be more reliable, manufacturable and to yield an improved sensor.